The present invention relates to a communication system for transmitting and receiving divided pieces of data simultaneously by different transmission paths, and particularly to a communication system, a transmitting device, a receiving device, a processing method therein, and a program for making a computer carry out the method.
A frequency diversity system is a method that transmits an identical signal by a plurality of different carriers, and selects or synthesizes the carriers on a receiver side, thereby improving characteristics (see Japanese Patent Laid Open No. 2000-201130 (FIG. 5), for example). However, this frequency diversity system has a problem in that the transmission rate is not improved that much, considering the hardware resources put in to deal with a plurality of different carriers for simultaneous transmission of an identical signal. With current technology, for example, the maximum radio transmission speed in an IEEE802.11a standard by a working group of an IEEE (Institute of Electrical and Electronics Engineers) 802 standardization committee, for example, is 54 Mbps (bits/second), which cannot be said to be sufficient as compared with wire transmission speeds.
Hence, transmission path multiplexing by simultaneous transmission and reception of a plurality of radio signals is considered. In this case, original data to be transmitted is divided into a plurality of pieces, and these divided pieces of data are transmitted by respective different transmission paths. For example, when a plurality of radio signals in different channels in an identical frequency band or channels in different frequency bands are used simultaneously, since performance is determined by the transfer characteristics in each channel, even if the transmission speed of one channel is lowered due to multipath effects or the like, performance deterioration can be minimized by using the other channel. In addition, when radio waves are sufficiently reflected or scattered due to a multipath, this can be taken advantage of instead to improve performance by using an identical channel in an identical frequency band.
However, when radio signals in different channels in an identical frequency band or channels in different frequency bands as different transmission paths are used, the number of channels, which number corresponds to the number of pieces of data to be transmitted simultaneously, is required. Thus, there may be an inconvenience from a viewpoint of use efficiency. On the other hand, the use of an identical channel in an identical frequency band as different transmission paths can be dealt with in theory by increasing the number of transmitting and receiving antennas and RF circuits in the identical frequency band. However, a data separation process on the transmitter side becomes extremely complex as the number of pieces of data to be transmitted is increased, and therefore, the number of pieces of data to be transmitted simultaneously is strictly limited.
It is accordingly desirable to improve the transmission rate while limiting the use of frequency bands in radio communications and alleviating the complications of the data separation process.